An air bag apparatus is disposed in front of a driver's seat or a passenger seat or disposed on the side of the driver's seat or the passenger seat to moderate an impact that a passenger receives at the time of collision of an automobile. An acceleration sensor operates upon reception of an impact received when the automobile collides, and an air bag is operated to protect the passenger from the impact of the collision. This air bag apparatus is mounted on the assumption that an adult sits on the seat, and since an adult usually sits on the driver's seat, the air bag of the driver's seat may be operated automatically when receiving an impact of collision of the automobile.
However, a passenger does not necessarily sit on the passenger seat or the backseat. In such a case, it is not only useless to operate the air bag of the passenger seat or the backseat at the time of collision, but it can be dangerous because pressure is applied to the driver from the side or behind in some cases. Further, a child sits in the passenger seat or the backseat in some cases. In such a case, this is dangerous because the operated air bag may strongly hit his or her face, and it is desirable not to operate the air bag in some cases.
Even with a seated passenger, when the sitting position deviates from a normal sitting position such as when the passenger is sleeping or crouches forward, it is preferable that the air amount for the air bag is reduced or the air bag is not operated.
Therefore, in a vehicle such as a passenger car having an air bag apparatus, it is proposed to detect whether a passenger sits in the passenger seat or backseat, and whether the sitting state is normal, and to control the operation of the air bag apparatus in accordance with the detected information.
To detect whether a passenger is sitting in a seat of an automobile, there are conventionally proposed a structure in which a weight sensor is disposed in a seat portion of a passenger seat, and the weight when a passenger sits on the passenger seat is detected (see patent document 1, for example); a structure in which it is determined whether a child seat is mounted on a seat based on detection results of a sitting sensor incorporated in a seat surface of a seat; latch detection means for detecting whether a seat belt of a seat is latched, and using amount detection means for detecting the using amount of the seat belt, and which can clearly distinguish a case in which an adult is sitting in the seat and a case in which a child seat is mounted (see patent document, 2 for example); a structure in which a seat is provided at its substantially front surface with a sensor using a pyroelectric infrared radiation detector which senses a human body temperature of a passenger in non-contact manner, and it is detected whether there is a passenger on the seat by means of an output signal of the sensor (see patent document 3, for example); and a structure in which a plurality of antenna electrodes are embedded in a seat back of an automobile, electric field generating means for generating electric field are provided around the antenna electrode, and if a passenger sits in the seat, current flowing through the antenna electrode from the electric field generating means is increased allowing detection that a human body has approached the antenna electrode, and in which a detected combined pattern is compared with a previously stored pattern, and it is determined whether there is a passenger sitting in the seat and the physique of the passenger is also determined (see patent document 4, for example).    [Patent document 1] Japanese patent Application Laid-open No. 2004-284425((0010), (0025), FIG. 1 and the like)    [Patent document 2] Japanese patent Application Laid-open No. 2002-255010((0013) to (0014), FIGS. 1 and 2, and the like)    [Patent document 3] Japanese patent Application Laid-open No. 2002-234415((0001) to (0016), FIGS. 1 to 4, and the like)    [Patent document 4] Japanese patent Application Laid-open No. H11-198705((0017) to (0024), FIGS. 1 to 5, and the like)
According to the method of the patent document 1 using the weight sensor, since the weight sensor is operated also when baggage is put on a passenger seat or backseat, it is impossible to distinguish whether a passenger is sitting in a seat or baggage is put on the seat. Therefore, it is determined that a passenger is sitting in the seat also when a baggage is put on the passenger seat or backseat, the air bag is operated uselessly, and there is a danger that a passenger may lose his or her hearing ability due to abrupt expansion of the operated air bag, the air bag may strongly hit the passenger's face and may lose his or her sight. Further, when the sitting position is deviated from the weight sensor or when an infant sits in the child seat, the weight sensor does not detect the passenger in some cases. In such a case, it may adversely be determined that no passenger sits in the seat.
According to the method of the patent document 2 using both the sitting sensor and the seat belt detection, a passenger can not be detected correctly when the seat belt or the child seat is not used. When baggage is secured using the seat belt, there is an adverse possibility that the baggage is erroneously recognized as a passenger, and the air bag may be operated uselessly.
According to the method of the patent document 3 for detecting whether there is a seated passenger on the seat using the output signal of the pyroelectric infrared radiation detector sensor, the pyroelectric infrared radiation detector sensor is used, and the temperature variation is detected when a passenger gets on or off, and if a seated passenger slowly gets on or off, or if a seated passenger remains at rest, the pyroelectric infrared radiation detector sensor can not clearly detect a difference between a temperature of the passenger and a room temperature which is a background temperature.
According to the method of the patent document 4 for detecting approach of a human body using the antenna electrodes, the electric field generating means for generating electric field around the antenna electrodes is required, this complicates the structure, and there is an adverse possibility that the passenger detection apparatus is erroneously operated by an electric field from outside of the automobile and by an electric field from various electronic control devices in the automobile.